Furnace for treating zinc ores and other zinciferous material



April 15, 1930. A. ROITZHEIM ET AL 1,755,076

FURNACE FOR TREATING ZINC ORES AND OTHER ZINCIFEROUS MATERIAL Fliled April 23, 1926 3 Sheets-Sheet 1 April 15, 1930. A. RClTZHEIM ET AL FURNACE FOR TREATING ZINC ORES ANDOTHER ZINCIFEROUS MATERIAL I 5 Sheets-Sheet 2 Filed April 25, 1926 Patented Apr. 15, 193% FURNACE IFOR TREATINGZINC GEES AND OTHER- ZINCIFEROUS MATERIAL Application filed April 23, 1926, Serial No. 104,147, and in Germany November 13, 1925.

This invention relates to a method of and to a furnace for treating Zinc ores and other zinciferous material in vertical reduction chambers or muflies in a continuous working operation.

Attempts to solve the problem of producing zinc in vertical mufiies have been made for decades past and consequently numerous proposals have been made, part of which have merely been published whilst others have been tried in practice. Nevertheless the zinc industry throughout the world at present works for the most part with muflies arranged horizontally in the furnace. It follows from this that no practical solution of the problem has hitherto been found.

Why is this? The technical advance in metallurgy can only lie in the increased simplification of the apparatus in which the metallurgical processes are carried out and in the decrease in human labour.

When, in the history of zinc-production itwas first suggested to employ a vertical muffle instead of a horizontal muffle, it was probably primarily only due to the wish to reduce the action of the slags segregated from thecharge which, in horizontal muflies, destroyed the bottom of the mufiie too rapidly. Lately when the idea of vertical muffles was repeatedly reopened the obvious possibility of facilitating charging and discharging by means of a vertical muffle, was aimed at.

In the old method however the metallurgical treatment in vertical muifles was not rendered uninterrupted. The vertical muffle had to be opened at the top and at the bottom, on discharging. It was found that the work was far worse than in the old methods because the workmen who opened the lower muffle were exposed to a spray of incandescent slag mained, because destroyed muffles had to be replaced in the same way as in the case of horizontal mufi les. F or this purpose, in the case of vertical mufiies, the furnace had to be opened at the top and bottom at those places where the muflles had to be inserted. This entails considerable difliculties so that the superiority of the un nterrupted metallurgical treatment in the vertical muffle was again counteracted.

' The above-described difliculties however become excessive if it is necessary to employ muflies of a larger size in order to ensure a sufiicient daily production.

The weight of the muffies to be brought to incandescence in tempering furnaces could be overcome by mechanical means, but not the breaking out of the destroyed mufile. This necessitates the employment of very strong and courageous workmen.

The question might be raised as to whether this difficulty could not be overcome by bricking the muftles together. Proposals to this effect have already been made long since. However in view of the unavoidable movement of the furnace, expansion by heat, as well as the swelling and shrinkage of the refractory masonry, the walls of the muifles cannot be made tight in the vertical joints even by providing groove and tongue joints. Also the necessary, and even in the extreme case, still considerable thickness of the stone, conducts the heat far too badly as compared with thin walled clay muffies. Consequently brick muliles have also everywhere proved unsuccessful.

According to the invention the operation and the construction of the furnace are such that the same remains in operation for a prolonged period undisturbed by any replacement of the muffies, with continuously uniform firing, irrespective as to whether any muftles have become faulty and the furnace is only cooled down when a certain number (about to A) of the muftles arranged in the furnace have been destroyed. After complete cooling the muffles are removed from the furnace and cold mufiies, in an unburnt or initially tempered state, are freshly inserted, whereupon it is reheated for a new working operation. If, after a certain time, one or other of the muflles should become faulty, it is, instead of being charged with ore, filled with a refractory substance such as for example fire-clay or sand, and remains in the furnace. This is continued until the number of the faulty and therefore unproductive muflles has become so great that a further operation of the furnace would be uneconomical, whereupon the fire is drawn without regard to the number of muilles present which are still in a good condition.

By mounting the muffles in a cold state large muffle can be composed either of several adjacent small mutlles connected together horizontally by means of several tubular members so that the zinc vapours evolved can be removed through a flue to a common receiver in the front wall of the furnace, or the large muflle may be divided horizontally into separate parts or sections, the construction of which offers no practical difiiculties, these be ing then mounted in the furnace one above the other with horizontal joints. The weight of these muflles, as experience has shown, tight ens these joints which are smeared out by means of a friable mortar.

A weak point in vertical mufiles is in general, the carrying capacity of the refractory wall material. All vertical muffies have a tendency to belly out in the furnace. The prolonging of the life of the muflles under such conditions, to such an extent as to provide for a periodical process with practical success can only be solved by the insertion of skeletons or by forming the profile of the muflle of thin walls exposed to the fire and thick middle cheeks which are not directly exposed tothe fire and which, so to speak, form a spine for the muffle.

Only the periodical reinsertion of the muffles in the cold furnace allows such manipulations. By this means it is possible to employ muflles of a height of two or even three metres. If it were attempted to temper such mufiles outside the furnace and to insert them into the hot furna ce, then, owing to the highly irregular division of the material and to the non-uniform cooling", unavoidable stresses of the mufile would be produced in the mulfles during transport, which would lead to their cracking. The periodical process however affords a freedom in the shape of the muflle which would otherwise be impossible.

Inasmuch as in the new furnace only relatively moderate tenuperaturcs may prevail greater value must be attached to very uniform distribution of the temperature in that part of the muflie where the reduction of the ore proceeds i. e. the flame must be homogeneous in the combustion chamber between the individual mufiles and may not have any appreciable fall in temperature. This is best attained by adding the combustion air to the gas in stages and by correspondingly adjusting the flames.

The provision of the cold furnace with inullles in the cold state permits the insertion of fines for this purpose, between the outer walls of the muffles and enables the combustion air to be distributed along the path of the gas through inserted perforated tubes or hollow stones employed for the formation of the heating flues.

Owing to the fact that the insertion of the lines between the niuilles, has fixed the path of the fire, the further construction ofthe furnace becomes very simple.

A dome for the chamber in which the muffles are located is dispensed with. The muflies rest upon an iron supporting construction and carry their own top covers. Since tie mufiles, by means of interposed plates, form fines for the passage of the ileum, the channels for the admission and discharge of the heating and combustion gases can be united into a common masonry blocl: which also surrounds the gasproducers and the air preheaters for the combustion air. The surroundingwalls of the furnace are entirely devoid of fines and contain only inspection holes for the inspection of mur'lles. (inly the wall opposite the centre blocl: of each side contains a niche for the receiversfor condensing the Zinc vapours. The muflles are mounted entirely independently of the furnace masonry upon an iron supporting construction, which is protected from the action of the fire by a layer of fire clay or sand placed ata height of 0.420 metres outside the lower portion of the mufi'les.

Thus, the very essential conditions that the muffles remain entirely independent movement of the furnace brick work, that they are able to contract or ex Jaud entirely independently and that they are not exposed to any forces which may be produced by any displacement of the highly heated furnace brick work, are fulfilled, in a most simple manner. This circumsta ceis very important for the life of the inufile.

Without construction in the cold, the hue for the flame could only have'been conducted from one wall of the furnace to an opposite one. The muiiles would then be arranged between these two walls. The gas inlet and outlet would have been specially separated. As compared with this the concentration of the channel work in one block. constitutes an advance in the metallurgy of zinc, in r spect of heat utilization and construction;

By this arrangement of all the channels, of the air heating chambers, and of ie lire in one central furnace block, kind of heat accumulator is formed which compensate for fluctuations in the heat which are t duced by drawing the fires, char n fr I 1 I a b fuel and the like. This is a great advantage for the mufiles and contributes to prolonging their life.

When the mufiles are destroyed, the fire must be drawn and the furnace cooled until it is again fitted with new muffles. The heating of the muffles must proceed slowly. This is preferably effected by grate fires. Degasified carbon or coke is employed for the first heating serving to temper the muffies. The incandescent heat spreads slowly through the central block of masonry and as soon as this block has itself become incandescent, the heat is transmitted to the muffles. The muflles are thus heated very gradually and very uniformly, which takes about a week. When the muflles are at red heat, there is no longer any danger and new gas and combustion air can be introduced into the fines and the operation can be started.

The requisite heat for the operation of the furnace can be produced in the same grate as the preheatin In order uniformlyto spread the fire to the furnace, it has been found useful to distribute the combustion amongst four fires instead of one large fire. This uniform distribution of the fire is essential when reheating the cold furnace. It is of course possible to utilize these firings only as auxiliary firings which have merely the object of heating the furnace and the muffies and which are bricked off when the furnace has reached a red incandescent heat. The normal heating is then effected by spe cial gas inlet pipes to which combustible gas produced outside the furnace proper, is admitted.

In order more clearly to understand the invention reference is made to the accompanying drawings, which illustrate by way of example one embodiment of a zinc furnace with vertical reduction chambers suitable for carrying out the new method of operation, and in which r Fig. l is a longitudinal sectional elevation. On the left-hand side the section is through the centre of the muflles, whilst on the right-hand side the section is through the heating flues.

Fig. 2 shows at the left-hand side, a longitudinal section through the furnace of Fig. 1 along the lines 2-2 and on the right-hand side a view of the receiver side.

Fig. 3 is a lateral elevation of the broad side of a muffle on an enlarged scale (partly in section).

Fig. 4 is a top view, broken-olf on the left hand side. 1

Fig. 5 is a view of the narrow side (receiver side).

A indicates the ground of the furnace, B

is the working level for attending to the receivers and G is a charging stage. The furnace formed by the lateral surrounding walls U U and the two sides for the receivers VV W is divided int-o equal parts by masonry D. Four separate fires are arranged in this masonry for each half of the furnace. Only two, D and D are shown in the drawings. The firing may for example be of the water gas type. From each combustion chamber a vertical channel (E in Fig. 2) leads upwardly into a horizontal channel F and in the central wall D. Flues G lead from the horizontal channels F and F into the muffle chamber of the furnace and terminate in the uppermost flues between the muffies.

The air is preheated by the air heaters H H arranged in the masonry D and ascends in the channels J and J 2 from which distribution channels branch off into the heating flues. The air is distributed over the length of the heating fiues through the separating walls 19 constructed from hollow bricks and provided with openings m m m The gas entering the uppermost heating flue consequently does not immediately obtain the total air for combustion required, but only gradually. By this means a long flame is produced and detrimental blow pipe flames are avoided.

The burnt gases pass to the air heater H and H through the waste .gas channels L and L and play against the tubes N and N through which fresh air is admitted, and are then discharged through the outlets O and O The muffie chamber is supported by a scaffolding P consisting of iron carriers carried by columns in which openings are provided to correspond to the reduction chambers (muffies). The mufiies R- are mounted upon the scafiolding P independently of the surrounding walls of the furnace and of the central masonry block. The intermediate spaces from muffle to mufiie are filled up below with powdered fire clay and the like. This mounting allows the mufiies all movement due to heat expansion.

The mufiles are composed for example of six parts r r r r 7 T which abut against each other with horizontal joints. The number of the parts depends on the height of the mulfles. The individual parts of the muffles engage with each other by means of feather edges, said feather edges being pro vided with projections towards the heating flues, upon which projections are mounted the plates 79 or hollow bricks p forming the heating flues and at the top, the cover plates (Z. The cross-section of the muflles is longitudinal (Fig. 4) their walls are as thin as possible towards the heating side in order to enable the heat to penetrate easily. The front and rear walls which are vertical to the thin heating walls of each mufiie, are however comparatively thick and moreover in the centre of the cross-section, two or more thick transverse walls 9 are provided in order to provide the muffle by'means of a spine, with the necessary support in the fire. The inner space of the muffle is subdivided by these central transverse or. supportingwalls g. In order to enable thezinc vapours and reduction gases to pass from the thus pro 'ided divisions of each inufiie towards the one re ceiver V in the fr nt wall. of the mulile, these interior transverse walls a are provided with perforations 0 at the level of'the receiver. The receivers V are inserted into the walls of the mu'liles facing the front wall of the furnace- Their shape and their closure means are of the type usual in zinc furnaces. In order to protect the receivers V against the combustion gases they are surrounded with annular bricks in. In other respectsthe receivers are similar to those of ordinary Zinc furnaces, built into niches and provided in front with slots t for taking up the burning non-condensed gases and vapours which are conducted away through the channels 2.

The muffles terminate at the bottom in iron pockets T through which the ash descends continuously. The closure means for these pockets are formed by a trough s which may if desired be filled with water to seal off the air completely. From this trough the ash is removed as required.

The roof of the furnace is formed by the plates cl resting-on the upper edge of the reduction chambers, corresponding openings in the interior of the reduction chambers being left free. Above this are arranged the charging stage C formed by iron carriers or plates which also contain openings corresponding to the openings of the reduction chambers.

On restarting the furnace all reduction chambers and receivers and the tube N of the air heaters are changed. The reduction chambers are built up from the parts 1 which have only been preliminarily burnt and which are inserted into the furnace in a cold state in the manner shown in Figs. 3 to 5. A permeable construction of known type made from shaped pieces is located in the muffles for conducting the gases and zinc vapours into the receivers (not shown). After closing up all, the furnace is carefully heated up and when it has gradually been brought up to a red incandescent heat uniformly in all parts the muftles are slowly started, the charge being first poor in zinc and rich in reduction coal whereupon the zinc content is gradually increased until the normal charge is finally used.

In normal working, the muflles are charged at the top with a charge mixed with reduction coal at certain intervals after iron rods have been poked several times through the charge in the reduction chamber in various parts, in order to loosen the charge and to cause it to settle down. The fire is constantly maintained uniform so that the reduction chambers are kept as much as possible at the same temperature. The dezincing takes place continuously because fresh particles of the charge, after gradual preheating continually reach the zone of the maximum temperature and sink slowly therethrough. The speed of descent of the charge must be adapted to the dezincing and to the prevailing temperature. The zinc vapours are led away through the permeable constructions into the compartments formed by the transverse walls 9 of the reduction chambers and reach the receivers where they condense to liquid zinc, whilst the reduction gases accompanying the same, after having been passed through an iron drum in order to deposit the zinc dust, are burnt in air and conducted away or if desired are utilized unburnt. The collected zinc is tapped off as often as desired, normally once a day.

The ashes are discharged in suitable intervals from the trough s, or may be continuously removed by conveying devices. The furnace is operated continuously and without interruption in this manner. If, in the course of time, a muffle should become faulty so that zinc losses occur, it is filled with a different material and left. The remaining muilles are used until finally so many mufiles have been cut out that the further operation of the furnace becomes unremunerative, when the fire is drawn and the furnace is repaired.

Various modifications may be made in the above described process and apparatus with out departing from the spirit and scope of the invention. A short regular alteration (ca. each 20 minutes) from a very high te1nperature,(ca. 1 400 C.) to a low one (ca; 1 100 C.) may, too, be admitted. This change may take place at the whole furnace or between two compartments of the furnace alternatively. In the meaning of the present invention such type of heating is also representing a uniform one.

lVhat we claim is:

1. A zinc reduction furnacecomprising an enclosing masonry structure, a inultiplicity' of spaced, vertical, refractory mufiles arranged in said furnace, the muflles being supported independently of each other and of said masonry structure, a roof for the furnace formed by plates carried by the muffles, means for supplying heating gases to the flue spaces between the muflies, and means for supplying additional air to said flue spaces.

2. A zinc reduction furnace as claimed in claim 1 in which the vertical muflles are made in sections having bell-shaped ends, platesflue spaces, the flues and plates being alternately arranged to provide a tortuous passage for the heating gases.

4. A zinc reduction furnace comprising a multiplicity of vertical muflies, the muflles being formed in sections, each section being rectangular in shape and having thin side walls and thick end and transverse walls.

5. A zinc reduction furnace as claimed in claim 4, in which the transverse walls and one end wall of at least one section are provided with openings for escape of zinc vapor, and condensers connected to said end openings.

6. A sectional muffle for zinc furnaces each section being rectangular in shape and having thin side walls and thick end and transverse walls.

7. A zinc reduction furnace comprising an enclosing masonry structure a multiplicity of spaced vertical refractory muffles arranged in said furnace, the muffles being supported independently of each other and of said masonry structure, and means for supplying heating gases to the flue spaces between the mufHes.

8. A zinc reduction furnace as claimed in claim 7 in which refractory powdered material is located between the mufiies at their lower portions.

9. A zinc reduction furnace as claimed in claim 7 in which the mufHes consist of a plurality of adjacent tubes built up of individual sections, the exterior wall of one of said tubes having an opening, a condenser connector to said opening, the other tubes having openings at the level of-the condenser.

In testimony whereof, we affix our signatures.

ALEXANDER ROITZHEIM. WILHELM REMY. 

